The present invention relates generally to an apparatus and method for performing submerged arc welding. More specifically, it relates to an apparatus and method for delivering welding flux using a pinch valve to control the flow of flux to the arc.
Submerged arc welding is a type of welding where the arc is completely submerged in a covering of granular fusible flux. The flux protects the molten weld puddle from atmospheric contamination. Submerged arc welding systems, like other types of welding systems, typically include a welding power supply, a wire feed control and drive assembly and a welding torch. In addition, submerged arc welding systems also include a flux system. The flux system holds and delivers the flux to the weld joint during welding. Flux systems typically are either gravity fed or pressurized (forced air) systems.
Flux systems typically include a hopper having a chamber for holding the flux, a feeding device (typically a tube connected to the torch) for delivering the flux from the hopper to the arc, and a flux valve to start and stop the flow of flux from the hopper to the arc. Some flux systems also include a recovery system for recovering any unfused flux from the workpiece being welded.
There are basically two types of welding torch/flux feeding device combinations used in submerged arc weldingxe2x80x94side flux delivery systems and concentric flux delivery systems. Flux is delivered in front of the wire electrode in side flux delivery systems. In concentric flux delivery systems, flux is delivered concentrically around the wire electrode.
Submerged arc welding systems can be fully automatic or semi-automatic (also called manual). The entire welding process is automatically controlled in a fully automatic system. The welding torch can be automatically moved over a stationary workpiece or the workpiece can be moved automatically under a stationary welding torch. In a semi-automatic system, an operator adjusts the welding parameters during welding and manually moves the torch.
A typical submerged arc welding pass includes the following steps. The first step is called pre-flux. The flux valve is opened and flux flows from the hopper to the weld joint during pre-flux. The arc, however, is not started and the torch is not moving during pre-flux. The flux continues to flow and pile up under the torch until the pile of flux located on the weld joint backs up into the torch (and feeding device). At that point, the flux in the flux valve and feeding device is substantially stationary and no more flux flows from the hopper even though the flux valve is open.
Following pre-flux, the arc is started and welding begins. The torch and accompanying arc move along the weld joint. Flux flows through the flux valve and feeding device to the torch as the torch moves forward. Movement of the torch is stopped at the end of the weld joint. The flux continues to flow until it once again piles up under the torch and backs up into the torch. The flux valve is closed after the flux has substantially stopped flowing. Finally, the arc is stopped and the welding pass is complete.
The flux valve is typically located in-line between the hopper and the arc. The valve opens and closes to release flux from the hopper chamber to the arc. Prior art flux valves used in automatic submerged arc welding systems suffer from many problems. These valves typically are complex devices having many parts. All of the prior art flux valves, in addition, have moving valve parts that come in contact with the flux itself. The granular flux passing through these valves can clog the moving parts or cause these parts to wear out prematurely.
A common type of prior art flux valve in use is the guillotine valve. In a guillotine valve, a thin blade slides on a track in and out of the flux flow path. The guillotine valve is well suited for this application because the blade""s thin edge easily knifes through the stationary flux that backs up into the flux valve and feeding device after the torch stops moving. The guillotine valve suffers from several problems however. Many of the moving parts of this valve are in continuous contact with the granular flux. This results in excessive wear and tear on those parts and the valve itself.
Flux also gets on to the blade""s track as the blade moves back and forth. This flux can interfere with movement of the blade, eventually resulting in failure of the valve. Additionally, a portion of the flux that collects on the track is continuously pushed off of the track and expelled from the flux system by the moving blade. An extra recovery system is required to collect this expelled flux.
What is desired, therefore, is a valve structure that is simple with few parts. It is also desirable to have a valve that is sealed so that no flux can escape from the flux system. It is further desirable to have a flux valve with no moving parts in contact with the granular flux material. Finally it is desirable to have a valve that can open and close easily when the granular flux passing through the valve is stationary (or substantially stationary).
According to a first aspect of the invention, a welding apparatus for submerged arc welding includes a welding power supply, a wire feeder in electrical communication with the power supply, a torch in electrical communication with the power supply, and a flux system. The torch is adapted to deliver an electrode wire from the wire feeder to an arc. The flux system has a flow path for delivering flux to the arc and includes a pinch valve disposed to open and close the flow path.
In one embodiment, the pinch valve includes an elastomeric tube defining a portion of the flow path and in another embodiment the elastomeric tube is made of latex.
In other embodiments, the pinch valve includes an elastomeric tube made of latex defining a portion of the flow path and a pneumatic actuator disposed to open or close the flow path. In alternative embodiments an electrical actuator is disposed to open or close the flow path.
According to a second aspect of the invention, a flux system for supplying flux to a welding arc along a flow path includes a hopper having a discharge port, a feeding device, and a pinch valve. The feeding device is connected to the discharge port and defines a portion of the flow path. The pinch valve is in the flow path and opens and closes the flow path.
In one embodiment, the pinch valve includes an elastomeric tube defining a portion of the flow path and in another embodiment the elastomeric tube is made of latex.
In other embodiments, the pinch valve includes an elastomeric tube made of latex defining a portion of the flow path and a pneumatic actuator disposed to open or close the flow path. In alternative embodiments an electrical actuator is disposed to open or close the flow path.
According to a third aspect of the invention, a method of submerged arc welding includes actuating a pinch valve to open a flux flow path, delivering flux along the flux flow path to submerge an arc, supplying weld power to the arc, and feeding an electrode wire through a torch to the arc.
In one embodiment, the pinch valve is pneumatically actuated to open the flux flow path.
In a second embodiment, the method includes moving the torch along a weld joint and actuating the pinch valve to close the flow path after the torch stops moving along the weld joint. In a third embodiment, the method includes moving the torch along a weld joint and actuating the pinch valve to close the flow path when the flux in the flow path is substantially stationary.